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How many hours of light do I need for veg growth?


Member of the Month: Aug 2013
i have used glr for the whole of this grow im doing and im getting amazing results, my clones grew like crazy and my seedlings showed sex after 2 weeks, they where fem seeds but still good to know, ill be using glr for a few more days then im going to try the deminishing light schedule for flower, i think glr works a lot better with clones to start off with as it takes the seedlings time to be mature enough to benefit from the rapid growth.

glr method.
12 hours of light
5.5 hours of dark
1 hour of light
5.5 hours of dark,
then repeat.

what this method does imo is tricks the plants into thinking its starting to flower but by giving it the 1 hour of light during the 12 hour of off period it stops the plants flowering, they show sex and will show all the way through the grow, but they wont actually flower till you remove the 1 hour of light during the dark period, this also makes the plants start flowering quicker, pretty much strait away.

the only thing im unsure of and wont know till i flip the lights to flower is if the plants still stretch when flipped to flower, as they are basically growing rapid under glr this is then the stretch period they normally receive in flower, but the 1 hour of light prevents them from flowering, so will they still have some stretch when flipped to flower i dont know, but im going to find out,

duck man

New Member
I tryed 20/4 and all i got was a higher elec. bill, i'll be going back to 16/8 .Looking at the chart above that gives max root growth .Thanks for the chart


Member of the Month: Aug 2013
give glr a try, over a 24 hour period your only using 13 hours of electric, which is keeping costs and equipment life down, now im not sure that the statement plants push production to the roots during dark period, i say this as i had a power cut the other day and the lights where off for 22 hours, when they came back on i was shocked at what i saw, all my plants grew between 2 and 3 inches, this was more growth than i had seen in a whole week, so these plants do grow in the dark, maybe this is why the plants stretch when they are flipped to 12-12, the extra dark forces them to grow, till i seen this for my own eyes id say the roots grew in the dark, but after looking at my plants after a power cut i was expecting wilting plants, but i came back to really healthy and taller plants, so they do grow in the dark and a lot by the looks of it, i had taken pictures the night before the power cut so i know they grew at least the much, the 2x 2ltr dwc hempie had grown 3 inches each, so the plants still grow in the dark.

like i said ive been using glr for the whole of this grow, and i have found the clones grow a lot quicker from day 1 after rooting, the seedlings take a week or 2 to catch up growth wise, after that the grow like crazy, it cuts down the veg time, all my seedlings showed sex at 2 weeks old instead of 4 weeks old, then when i flipped the lights to flower 12-12, the plants went into flower a whole lot quicker,

glr really works, but the best part is it keeps the costs down and the temps down as the lights are on less so glr is working great for all my plants,


I noticed in the article, it was mentioned o avoid using ONLY HPS lighting... That's all I am currently using for my setup. How risky is it go try the GLR cycle with only using HPS?


New Member
Some growers prefer all HPS because of the stretchy growth in veg they say, its faster to finish your plants by shorting the veg time, I here its great in a small space and saves money HPS are cheaper than MH.


New Member
Hi NewbGrow,
Hps lighting is usually more suited to flowering as the lighting spectrum is an amber/red color which plants respond to in flower, and during Veg will grow abit slower than with a MH, or even CFL's for that matter!
You can buy a dual-spectrum globe for your HPS, or even just get about 4, 6500k CFL's.. They will Veg a plant well enough til youre ready to use the HPS for flower. Ive not used the GLR yet, so Id assume that a light source will still grow a plant, but i still think it maybe slower during veg??? Hope it helps ya some mate? Smokemup..


New Member
plants will double in size when you put them in flower is my general rule, how big do you want them to get?


New Member
Does anybody have any advice about my light cycle?I would like to go from a 24 veg cycle to 18/6 veg cycle.Is that possible to accomplish without stressing plants out ?They have been in veg for three weeks.:hmmmm:


New Member
You can do it all at once or a little each day until you get the the 18 hours. Your plant will be fine.


Member of the Month: July 2012, July 2014 - Nug of the Month: July 2012
I vote for Gas Lamp Routine! I have used it for about 4 grows now, and overall it is the best lighting schedule for veg in my opinion. Less electricity used which means lower costs on the bill, less light stess to the plants and overall it seems like the plants grow just as fast, but flower much faster using the GLR in veg. I will never use anything else for this, have run sativa's, indica's and hybrids under this and they all have turned out amazing. I have even vegged clones with GLR and currently have 2 mothers at about 4 months old under GLR... definitely the only way to veg for me. :)


New Member
Personally I use the gas lantern routine and have had great success and growth. plus my plants hardly have a deficiency. I know that could be due to me growing style but i feel they are able to use large amounts of nutrients i feed them in a shorter light period. after all they grow during night too. Gas Lantern Routine: Veg:: 12 on 5.5 off 1 on 5.5 off Flower:: week 1/2/3 12 on 12 off, then reduce by 30 mins every week following. Perfect :)

loc dogg

New Member
rite ive got 3 under a 600w mh there 27 days old and approx. 3/4 to a foot in height 16/8 the cycle when should I bang the HPS up reply fast please!!!


Member of the Month: Aug 2013
what you mean mate, are you asking when to go 12-12 with the hps,

well if the plants are 1ft now and you flip to 12-12 now then you will have plants between 2 and 3ft when harvested depending on strain,

if i had 2 lights id switch to hps around week 1 of flower, so if you think your plants are big enough now to go 12-12 which you can do at any time and even from seed, or you can wait until the plant is mature enough before switching to 12-12, the plants are mature enough either when they show sex or when the nodes are not growing opposite each other, so instead of having 2 branches oppostie each other on the stem and branch you will have 1 branch growing one side of stem and another slightly further up the stem, sort of staggered branches

but you can flip to flower as soon as you like, id switch to 12-12 with the mh and around day 7 to 10 of 12-12 id then put the hps up,

you also need to change the nutes to flower schedule feed so id feed just water for 2 feeds so the plant uses whats up in the soil if your growing in soil then start with the flower feed around week 1 of 12-12,

so its really up to you my friend, you can grow 12-12 from seed if you like and get a low yield but it is possible, a lot of growers do this with sea of green grow,

if you need a response fast then you can drop me a pm as i check in on many journals so takes time to get through them all, but flip to 12-12 when ever your ready, the plants wont start flowering until their actually mature enough so you might not notice any flowers forming until week 2 of 12-12, but i use a dual spectrum hps so dont need to change bulbs, but if i did use a mh bulb for veg and hps for flower id flip to the hps around day 7 to 10 of 12-12.

feel free to pm me and ill get back to you much quicker, if you could get some pics up of the plants then it may help us give you better advice and guidance,


New Member
I have a question mildly related to light levels (can't post a new thread yet as I'm a newbie). Anyway, I am growing mmj in natural light outdoors. Sometime later this month, I'll manage to get some plastic over the frame, turning the growing area into a greenhouse, so that the plants will have a chance to mature bud after frost hits the mountains. I just visited this forum for the first time today and got some much needed information about how to start clones - and will be doing so later today.

I am very electrically challenged - meaning that I have only 840 watts of solar panels on my roof and have to limit my electrical use. So, there is absolutely no possibility of extending the light season with my clones. Therefore, my clones will start producing bud in about a month, when natural light goes to 12/12. It is my intention to keep my clones growing throughout the winter and to possibly start getting more buds for actual harvest during the spring equinox. I am going to build a rocket mass heater in the greenhouse. I am also planning to clone from clones to have a continuous harvest of small edible greens through the winter.

Should I clip off any buds that get started in September from the small clones? Does it hurt the plant to allow the still small clone to produce bud to harvest? The plants I have out there right now are in full vegetative state - not a bud in sight - and every one of them had buds on them last spring. I purchased the plants as clones from someone who grew them under lights and the minute I brought them home, the reduced light forced them into bud stage. But, eventually, I presume as the summer light increased, they stopped making buds and went back to becoming decent sized plants. Any idea how it's going to work going into the fall with reduced light levels? TIA for any help on this.


Member of the Month: Aug 2013
Hi mate,
welcome to 420mag,

ok so you want to leave plants outdoors in a greenhouse and try and get them to veg again, without any form of lighting this is not possible, any plants outdoors will flower then die at the end of the season, to get plants back into reveg from flowering you need to give the plants longer day hours, ive revegged many strains and continue to do so,

so if you take a clone in flower then you need to give it a veg light schedule around 18-6 or more is best, if you wanted to stop a clone flowering and keep it growing for next season then again you need more light hours than dark.

so the big plants will bud and die due to the end of the flowering season, if the clones dont receive any light they will also do the same outdoors,

so i take it you are going to let the big plants flower and you will then harvest them and the clones you want to keep for next season.

well you have a couple of options, first of all the clones will need a good amount of light to get them to root, anything 18 hours or more of light per 24 will help them grow roots and become viable clones.

you also need to consider outside temps in the tent if they go to low you will lose the clones, but sounds like you got the heat covered,

you need to find a way of getting the clones into veg for a few weeks before they go back to 12-12 else they just wont grow and you will be lucky to get anything from them.

so id let the big plants flower and if the 1st set of clones are big enough you can flower them, but without a veg period the clones wont grow enough to be able to produce more clones.

so you either need to keep the first clones for next season or give them some veg time soon, which is not possible while the bigger plants are flowering off, unless you take the clones in doors.

the clones will need to go back into veg to be of any use to you, you dont need big powerful lights to do this, all you need is a couple of 23watt cfls, the compact flourecent lights, the type you have in your house, they need to be the 6400k rating and not the orange 2700k lights,

you will need to get the clones to veg for at least 3 or 4 weeks before you can take clones from them else they just wont be big enough to produce clones.

so anythign 18 hours and above per 24 will get them back into veg and get them growing again and you will then be able to grow them and take more cuttings, without doing this you wont produce any more clones or keep them in veg long enough to be of any use.

their is how ever a cheap option of vegging plants, its called the gas lantern routine, this could even be set up outdoors as long as you didnt have any plants in flower as its a veg schedule,

now the gas lanter routine is basically 12 hours of light followed by 12 hours of dark, but in the middle of the dark period you give them just 1 hour of light,
so lets say you flowered the big plant off and wanted to grow the clones outdoors even though natural light is basically 12-12.
well glr is this schedule
12 hours of light
5 and half hours of dark
1 hour of light
5 and half hours of dark,
then repeat

so if you wanted to grow them outdoors and you had the clones in veg then all you would need to do is put a low watt light up and a timer so it just comes on for 1 hour, you would have the daytime hours to give light during the day, so to stop them going into flower you need to interupt the night cycle with at least 1 hour of light in the middle of the dark period,

glr is one of the best lighting schedules you can use, plants grow like crazy under it as they think their in flower so have the rapid growth due to them been under 12-12 but by providing 1 hour of light in the middle of the dark period your actually stopping the flowering hormones from building up so the plant dont go into flower until you remove the 1 hour of light,

so using glr you would just be using 1 hour of electric, you would just need 1 or 2 low watt cfls or flourescent lights, as long as the plants get the 1 hour of light then they will stay in veg,

but to get the clones to root you would need more than glr schedule, so for this you could take the cuttings and use a desk lamp in your property and have it either on 24 hours a day or on for 18 hours a day or more, if you use the low watt cfs or flourecent strip lights then that would keep costs down,

you could even use glr indoors but you would need to provide 12 hours of light followed by 5.5 dark, 1 hour light, 5.5 dark and repeat for as long as you want to grow them for.

glr is the cheapest schedule to use and probably the quickest way to grow plants, they will show sex sooner and look like their going into flower but their not and wont flower under glr until you remove the one hour of light during the middle of the dark period,

so you have a couple of options, first of all you need to root the clones so will need 18 hours of light or more per day to promote the roots to grow,

once the clone is rooted you can either keep them under 18-6 using cheap cfls of a low watt or you could use glr 12 hours of light, 5.5 dark, 1 hour light, 5.5 dark then repeat, again this is a cheap lighting option, cfls will keep the plants in veg and allow you to keep them growing until you put them back outdoors when the day and night period is nearing a veg schedule.

or if you have got the clones and the big plant has flowered then you could set up a couple of cfls outside near the plants and just run the lights for 1 hour during the middle of the night period, this will just cost you 1 hour of electric for a couple of cfls, then once your over the flowering period you could leave the lights off and let nature keep them in veg.


New Member
Thank you for the reply, DonPaul. I'm delighted to learn about the one hour of light to stop flowering. It isn't a matter of cost of electricity. It's a matter of not having it. I live off grid and make my own. I have a very limited amount. So, it sounds to me like I had better start as many clones as I possibly can right now, while I still have more than 12 hours of daylight and then plan to use the one hour of light approach to keep them alive and growing until spring. It also sounds like I'd better buy some more seeds and try to save some seeds again. I did that last summer, collected more than 2000 seeds, and then last spring planted 100 only to have none of them germinate.


Member of the Month: Aug 2013
thats not good with the seeds, how come you didnt have many germ, was they seeds you got from your own plants or off a mate, the best method is planting them direct in soil then water them every few days until they grow,

the gas lantern method works well and plants will get big using glr, its a great schedule for regular plants, as long as you give them 1 hour of light in the middle of the 12 hour dark period then they will stay in veg until you want to flower them,

so yep id start with the clones now so they got a good chance of rooting, i take it you use rooting gel or powder and use a dome to keep humidity around 100%, then you should have no problems getting them to root, the more light they get the better, even if its just in a room with a light on or near a table lamp, its not ideal but any light is better than no light, cfls are great for growing with, i use them still now to start my plants and clones under, low watts and perfect for these plants,

all you can do is see how you get on with the clones and see if they root, then go with the gas lantern routine and that will keep them in veg until you remove the 1 hour of light, they might look like their starting to flower but their not it will just be the clones showing sex so as long as you give them 1 hour of light during the dark period then they wont go into flower until you want them to, i think that might be your best option at keeping electric costs down,
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